Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the zoom lens, which are suitable for, for example, a broadcasting television camera, a cinema camera, a video camera, a digital still camera, a monitoring camera, and a silver-halide film camera.
Description of the Related Art
In recent years, a large-sized solid state image pickup element has become widespread in order to obtain an image having high image quality and a shallow depth of field, but a zoom lens is required to become much smaller in order to avoid an increase in size of an entire camera system. In particular, a zoom lens having a wide angle of view at a wide angle end tends to have a larger front lens diameter, which greatly affects a weight of the zoom lens, and hence a wide-angle zoom lens having a small front lens diameter is desired.
Hitherto, as a small-sized zoom lens capable of efficiently securing a magnification-varying ratio, there is known a zoom lens including lens units having positive, negative, and positive refractive powers, which are arranged in order from an object side. For example, in Japanese Patent Application Laid-Open No. 2015-22146, there is disclosed a zoom lens including lens units having positive, negative, and negative refractive powers, a stop, and a lens unit having a positive refractive power, which are arranged in order from the object side. The zoom lens has a half angle of view of about 40 degrees at a wide angle end, and includes a first lens unit and a fourth lens unit, which are fixed, and a second lens unit divided into lens units having negative and positive refractive powers. In Japanese Patent Application Laid-Open No. 2009-128620, there is disclosed a zoom lens having a half angle of view of about 40 degrees at a wide angle end, and including lens units having positive and negative refractive powers, a stop, and lens units having positive, negative, and positive refractive powers, which are arranged in order from the object side, the first lens unit and the fifth lens units being fixed.
As a zoom lens having a wide angle of view and a high zoom ratio, there is known a so-called positive lead type zoom lens including a first lens unit having a positive refractive power, which is configured not to move during zooming, a second lens unit having a negative refractive power, which is mainly responsible for zooming, and lens units on an image side of the second lens unit, at least one of which is configured to move during zooming. Further, as a positive lead type zoom lens having a wide angle of view and a small size, there is known a zoom lens of a so-called three-unit inner focus type in which the first lens unit includes a 1a lens unit having a negative refractive power, a 1b lens unit having a positive refractive power, which is configured to move in order to achieve in-focus, and a 1c lens unit having a positive refractive power.
In Japanese Patent Application Laid-Open No. H06-242378, there is described a zoom lens having a zoom ratio of about 8× and a photographing angle of view of about 87 degrees at a wide angle end, and including, on the image side of a second lens unit, a third lens unit for correcting an image plane variation accompanying zooming, and a stop configured not to move during zooming. In Japanese Patent Application Laid-Open No. 2014-63026, there is described a zoom lens having a zoom ratio of about 11× and a photographing angle of view of about 76 degrees at a wide angle end, and including, between a second lens unit and subsequent lens units, a stop configured to move during zooming.
An image pickup device, e.g., a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS), which is used in an image pickup apparatus, e.g., a television or cinema camera serving as a professional moving image pickup system, has a substantially uniform high resolution over an entire image pickup range. Therefore, a zoom lens used in the moving image pickup system is required to, for example, have a substantially uniform resolution with a high resolution over an entire image plane from an image plane center to an image plane periphery.
As a zoom lens that satisfies those requirements, a positive lead type zoom lens in which a lens unit having a positive refractive power is arranged closest to an object side has been known (Japanese Patent Application Laid-Open No. H06-242378, Japanese Patent Application Laid-Open No. 2007-316288).
In Japanese Patent Application Laid-Open No. H06-242378, there is described a zoom lens including, in order from an object side to an image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive or negative refractive power, and a fourth lens unit having a positive refractive power. The second lens unit and the third lens unit are configured to move during zooming. The first lens unit includes, in order from the object side to the image side, an 11 lens sub unit having a negative refractive power, a 12 lens sub unit having a positive refractive power, and a 13 lens sub unit having a positive refractive power, and the 12 lens sub unit is configured to move during focusing.
In Japanese Patent Application Laid-Open No. 2007-316288, there is described a zoom lens including, in order from an object side to an image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, a fourth lens unit having a positive refractive power, and a fifth lens unit having a positive refractive power. The second lens unit and the fourth lens unit are configured to move during zooming. The fourth lens unit is configured to move during focusing.
In addition, in Japanese Patent Application Laid-Open No. 2007-316288, there is described a zoom lens including, in order from an object side to an image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a positive refractive power. The second lens unit and the fourth lens unit are configured to move during zooming. The fourth lens unit is configured to move during focusing.
Hitherto, as a small-sized zoom lens capable of efficiently securing a magnification-varying ratio, there is known a zoom lens including lens units having positive, negative, and positive refractive powers, which are arranged in order from the object side. There is also known a zoom lens having a small front lens diameter when a wide angle is achieved, and including lens units having negative and positive refractive powers, which are arranged in order from an object side.
For example, in Japanese Patent Application Laid-Open No. 2009-92922, there is disclosed a zoom lens having a half angle of view of about 44 degrees at a wide angle end, and including lens units having positive, negative, positive, and positive refractive powers, which are arranged in order from an object side, the first lens unit and the third lens unit being fixed. In Japanese Patent Application Laid-Open No. 2007-193173, there is disclosed a zoom lens having a half angle of view of about 41 degrees at a wide angle end, and including lens units having negative, positive, negative, positive, negative, and positive refractive powers, which are arranged in order from an object side to an image side, the first lens unit, the third lens unit, and the sixth lens unit being fixed.
In the zoom lens configured to conduct zooming by moving the second lens unit having a negative refractive power toward the image side, in which the first lens unit having a positive refractive power is configured not to move for zooming, an off-axial ray having an intermediate focal length affects determination of an effective diameter within the first lens unit. Therefore, in Japanese Patent Application Laid-Open No. 2015-22146, a combined focal length after the second lens unit is made to be telephoto, and an off-axial ray angle between the first lens unit and the second lens unit is made to be gradual, to thereby suppress an increase in effective diameter of the first lens unit. The lens units after the second lens unit are made to be telephoto, but a principal point of the first lens unit is pushed to the image side, and a wide angle is achieved for a focal length of the entire system of the zoom lens. However, zooming is conducted with only the lens units on the object side of the stop, a distance from the first lens unit to the stop becomes longer, and an entrance pupil becomes longer, and hence the diameters of the first lens unit and the second lens unit tend to become larger. In Japanese Patent Application Laid-Open No. 2009-128620, the second lens unit is configured to move toward the image side, and the third lens unit is configured to move toward the object side. The stop is arranged between the second lens unit and the third lens unit, and is fixed during zooming, but can be pulled away from the third lens unit at the wide angle end and pushed to the object side to shorten the entrance pupil, which facilitates suppression of an increase in diameters of the first lens unit and the second lens unit. However, in order to greatly move the third lens unit and the fourth lens unit toward the object side during zooming, the third lens unit and the fourth lens unit are positioned near the image side at the wide angle end, and are not suitable as exchangeable lenses due to a short back focus.
With the positive lead type zoom lens having the above-mentioned structure, it is relatively easy to realize a wide angle of view, but in order to realize both high optical performance and downsizing, it is important to appropriately set refractive power arrangement of the lenses. In particular, an off axial ray passes through the first lens unit, which is closest to the object side, at a position farthest from the optical axis. Therefore, in order to realize both the optical performance and the downsizing, it is important to appropriately set a refractive power and a configuration of the first lens unit.
In the zoom lens described in Japanese Patent Application Laid-Open No. H06-242378, the stop is arranged on the image side of the second and third lens units, which are responsible for zooming, and hence a stop diameter is fixed during zooming, which facilitates mechanism control. However, the stop is away from the first lens unit, resulting in an increase in lens diameter of the first lens unit or an increase in number of lenses or number of aspherical surfaces. In the zoom lens described in Japanese Patent Application Laid-Open No. 2014-63026, the stop, which is configured to move during zooming, is arranged between the second lens unit and the third lens unit in a manner that is advantageous to downsizing. However, the small refractive power of the first lens unit disadvantageously causes an increase in size in achieving a wider angle of view. Further, only the second lens unit is mainly responsible for zooming, and hence a movement amount of the stop is disadvantageously increased in order to achieve both the downsizing of the first lens unit and the high zoom ratio.
In the positive lead type zoom lens, in order to obtain high optical performance over an entire object distance while securing the downsizing of the entire system of the zoom lens and the higher zoom ratio, it is important to appropriately set respective components that form the zoom lens.
For example, it is important to appropriately set a zoom type (including the number of lens units and signs of the refractive powers of the lens units), a focusing method, and the like. In particular, it is important to reduce an aberration variation accompanying focusing, and in order to obtain high optical performance over the entire object distance, to appropriately set selection of a lens unit (focus lens unit) for focusing, a lens configuration of the focus lens unit, and the like.
When the setting of those is not appropriate, the entire system of the zoom lens is increased in size to achieve the higher zoom ratio, or variations of various aberrations accompanying zooming and focusing become larger, which results in extreme difficulty in obtaining high optical performance over the entire zoom range and the entire object distance.
In the zoom lens configured to conduct zooming by moving the second lens unit having a negative refractive power toward the image side, in which the first lens unit having a positive refractive power is fixed during zooming, the off-axial ray having an intermediate focal length affects the determination of the effective diameter within the first lens unit. Therefore, in Japanese Patent Application Laid-Open No. 2009-92922, the combined focal length after the second lens unit is made to be telephoto, and the off-axial ray angle between the first lens unit and the second lens unit is made to be gradual, to thereby suppress an increase in effective diameter of the first lens unit. The lens units after the second lens unit are made to be telephoto, but the principal point of the first lens unit is pushed to the image side, and a wide angle is achieved for the focal length of the entire system of the zoom lens. However, as many as six to seven component lenses that form the first lens unit are arranged in order to push the principal point of the first lens unit to the image side, with the result that the first lens unit is disadvantageously heavy.
In Japanese Patent Application Laid-Open No. 2007-193173, the lens unit having a negative refractive power is arranged closest to the object side, and hence a wide angle is achieved for the entire system of the zoom lens with a small number of component lenses that form the first lens unit even when the lens units on the image side of the second lens unit are made to be telephoto. However, the fourth lens unit on the image side of the stop is configured to greatly move toward the object side during zooming, and hence an F-number at a telephoto end is as large (dark) as about 4.7 to about 5.1 with respect to a zoom ratio of 3×.